Rounded end halogen lamp with spiral exhaust tube and method of manufacutre

ABSTRACT

An incandescent lamp of the tungsten-halogen type having an envelope of an aluminosilicate glass comprising in percent by weight SiO2 between 59 to 70, Al2O3 between 10 to 20 and BaO between 7.4 to 28 and having a coefficient of expansion between 36 and 40 X 10 7 per *C and a tungsten filament connected to lead wires which are directly sealed into the envelope. One end of the lamp envelope is rounded and the other end contains the seal and the tipped-off residue of an exhaust tube. Enclosed in the tipped-off residue is a spiral of tungsten wire which keeps the exhaust tube open during the lead wire sealing operation.

United States Patent Main ROUNDED END HALOGEN LAMP WITH SPIRAL'EXHAUST TUBE AND METHOD OF MANUFACUTRE [75] lnventorz' Robert N. Malm, Willoughby, Ohio- [73] Assignee: General Electric Company,

Schenectady, NY. v

[22] Filed: Dec. 18, 1972 [21] Appl. No.: 315,772

- [56] "Re ferencesCitecl UNITED STATES PATENTS 2/1970 Dumbaugh ..3l3/22l' 2/1958 Dorsey ..3l3/315 Mar. 19, 1974 Primary Examiner-Herman Karl Saalbach Assistant Examiner-Richard A. Rosenberger Attorney. Agent. or Firm-Emil F. 505, Jr.; Lawrence R. Kempton; Frank L. Neuhauser [5 7] ABSTRACT An incandescent lamp of the tungsten-halogen type having an envelope of an aluminosilicate glass comprising in percent by weight SiO between 59 to 70, A1 0 between 10 to 20 and BaO between 7.4 to 28 and having a coefficient of expansion between 36 and 40x10 per C and a tungsten filament connected to lead wires which are directly sealed into the envelope. One end of the lamp envelope is rounded and the other end contains the seal and the tipped-off residue of an exhaust tube. Enclosed in the tipped-off residue is a spiral oftungsten wire which keeps the exhaust tube open during the lead wire sealing operation.

10 Claims, 9'Drawing Figures EXHAUST TUBE AND METHOD OF MANUFACUTRE 7 BACKGROUND OF THE INVENTION 1. Fieldof the Invention The invention relates to tungsten-halogen incandescent lampshaving a rounded end type of envelope of ahigh temperature glass and a method of manufacture therefor. More particularly, the invention relates to a lamp construction which has a spiral of tungsten wire embedded in the tipped-off residue of an exhaust tube, said spiral keepsthe exhaust tube open during the lead wire sealing operation.

2. Description of the Prior Art Although not necessarilylimited thereto, the invention has particularapplication to and will be described with reference to miniature incandescent lamps used in medical and optical instruments.

Various medical and optical examining instruments require uniform illumination, that is, illumination free of light distortion. Inorder to obtain this type of light, lamp envelopesare'made with dome-like rounded ends and, in some'cases, have ailens integral with the domelike end. The requirementof distortion-free light limits the lamp construction in that thelocation of the exhaust tube must either'be at the end of the bulb opposite the rounded end or in the side of the bulbfSidetubulated bulbs-are expensive to make andhave the added disadvantage of increasing the size of the instrument in which the lamp is used.

The alternative location is "the end opposite "the rounded end whichcontains the hermetically sealed lead wires. Attempts to position or attach the exhaust tube in the area of the sealed lead wires have lead to difficulties in'keeping the exhaust tube open. To a great extent, this problem is due to the fact that the lead wires are directly sealed to the envelope. Direct sealing operation thereby increasing the probability of closing the exhaust tube.

Not only is itdesirable to avoid light distortionfrom deformed orstriated glass, other interferences such as bulb wall blackening, caused by tungsten deposits are equally undesirable. Incandescent lamps, such as are described in greater detail in Fridrich et al. US. Pat. No. 2,883,571, eliminate bulb wall blackening through theuse of a tungsten-iodine regenerative cycle. Other halogens, such as bromine and chlorine, may also be used for regenerative cycle lamps.

' However, because of the differencesin coefficients of expansion between quartz or fused silica envelopes and lead wires in a conventional tungsten-halogen lamp, it became necessary to use foil portions as part of the lead wire conductor. The use of foil portions as a lead wire conductor component increased the size of the seal and, inturn, the overall size of the lamp tungsten-halogen SUMMARY OF THE INVENTION It is therefore an object of the invention to make a lamp with a minimum amount of light distortion. A further object of the invention is to be able to attach the exhaust tube to the envelope in the area of the lead wires seal without closing the tube. Still another object of the invention is to make a tungsten-halogen lamp without foil lead wire conductors. Another object of the invention is to make a halogen lamp of compact size. Yet another object of the invention is to devise a method of rapidly and effectively manufacturing rounded end lamps.

' Briefly stated, the objects of the invention are accomplished through the use of a tungsten spiral embedded in an exhaust tube in combination with certain aluminosilicate glasses and refractory metal lead wires.

A pre-formed rounded end bulb of a known glass comprising by weight percent between 59 and SiO,, IO to 10 A1 0 and 7.4 to 28 BaO having a softening point approximately 1 C and a coefficient of expansion between 36 and 40Xl0' C is positioned over a mount pin which holds an exhaust tube with a refractory metal spiral, such as tungsten, lightly embedded in the interior of the tube. The mount pin also contains two refractory metal lead wires to which is attached a tungsten filament.

Heat is applied to the open end of the bulb thereby collapsing the bulb around the lead wires and the exterior portion of the exhaust tube containing the tungsten spiral. The lamp is then flushed with an inert. gas to remove impurities and filled with a gas containing a halogen after which the exhaust tube is tipped off. Inthe event a lamp of increased pressure is desired, the rounded end of the'lamp can be immersed into a coolant such as liquid nitrogen and then tipped again to form a pressurized lamp.

BRIEF DESCRIPTION OF THE DRAWINGS I FIG. 1 is afront elevation view of one embodiment of the lamp of the invention;

FIG. 2 is a front elevational view of a lamp of the invention containing a lens;

FIG, 3 is a side elevation section view of the lamp of FIG. 2;

FIG. 4 illustrates the attaching of the tungsten spiral to the exhaust tube;

FIG. 5 shows the attaching of a filament to lead wires;

' FIG. 6 showsa method of sealing the lamp of the invention; I

FIG. 7 illustrates a method of flushing, filling and tipping the lamp of the invention;

FIG. 8 shows an additional tipping operation; and

FIG. 9 shows a method of cracking carbon from a halogen hydrocarbon.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. 1 of the drawings, the lamp 10 of the invention, therein illustrated, has an envelope 1 with a rounded end 12. Rounded end 12 is preferably free of all irregularities and striations so that there is a minimum amount of distortion of the illumination of filament 13. Distortion-free light of this kind is required in certain applications, such as medical and optical examining instrument lighting because the pattern of illumination is critical in diagnosis.

Tungsten filament 13 is attached to lead wires 14 by bending one end of the lead to form a hook or clamp as shown at location 15. In order to withstand the tungsten-halogen cycle, lead wires 14 are of a refractory metal such as molybdenum or tungsten. The lead wires are sealed to envelope 11 at area 16.

Heretofore, lead wires for tungsten halogen lamps could not be directly sealed to the envelope because the coefficient of expansion of a quartz or fused silica envelope, which could withstand the required bulb wall temperatures of the tungsten-halogen cycle, was significantly less than that of a refractory metal lead wire. Most tungsten-halogen lamp seals are therefore formed between extremely thin foil or foliated sections of refractory metals. Through the use of a high temperature aluminosilicate glass comprising by weight percent between 59 and 70 SiO 10 to 20 A1 and 7.4 to 28 BaO, it was found that an effective seal between the lead wires and envelope could be made directly, that is to say, without. the use of a foil conductor. Other properties of the glass are a melting point of approximately 1 100C and a coefficient of expansion between 36 and 40X 1 0" per C between 0 and 300C. The coefficients of expansion for molybdenum and tungsten are 52 and 46x10 7 per C between 0 and 300C respectively.

Located opposite rounded end 12 is tipped-off residue 17 of an exhaust tube. Contained within the tippedoff residue 17 is a spiral 18 of tungsten wire, which keeps the exhaust tube open to its full inside diameter during the lead wire sealing operation so that lamp can be subsequently flushed and filled.

FIGS. 2 and 3 of the drawings show another embodiment of the lamp of the invention. Lamp 19, which is similar to lamp 10 of FIG. 1, has an envelope 20 shaped such that rounded end 21 contains a lens 22 integral with the envelope.

Filament 23 is attached to lead wires 24 by forming a hook at 25. Spiral 26 is embedded in tipped-off residue 27 to keep the exhaust tube open during the lead wire sealing operation.

An example of a glass composition used in the lamp of the invention is, by weight percent, 62.0 SiO 17.2 A1 0 19.0 BaO, 1.5 CaO along with traces of ZrO and TiO. The lead wires of this particular lamp are 8-mil diameter molybdenum and the refractory metal spiral is made of tungsten.

The method used to manufacture lamps 10 and 19 is illustrated in FIGS. 4-8. As shown in FIG. 4, spiral 28 is positioned in exhaust tube 30 at one end. The outer surface of exhaust tube 30 is lightly heated by fires 31 to form exhaust tube assembly 32. This heating action softens the glass of the inner tube surface such that there is a small flow of glass between the turns of the spiral. It was found that, if the spiral had completely closed turns, difficulties were encountered in very small diameter tubes. Therefore, it is preferable to have at least some space between spiral turns.

Another step in the assembly process, mount making, is illustrated in FIG. 5. Filament 33 is attached to lead wires 34 by bending the lead wire to form a hook. Tool 35 is shown bending the end of lead wire 34 to hold one end of the filament in place. A like operation is performed on the other lead wire to form filament mount 41.

FIG. 6 shows head 38 which has an opening 36 for positioning exhaust tube assembly 32 and openings 37 for positioning lead wires 34. A pre-formed rounded end bulb 40 is positioned over filament mount 41 and exhaust tube assembly 32. Fires 42 are applied to the bulb to melt the glass around lead wires 34 and around the end of exhaust tube assembly 32 containing tungsten spiral 28.

Because of the difference in coefficients of expansion between the lead wires, 46 or 52 l0 per C for tungsten and molybdenum respectively, and the envelope, 36--40 l0" per C, sealing the lead wires directly to the envelope is a delicate process. The sealing fires must totally melt the glass so that it will flow and form a hermetic seal around the lead wires 34 and the exterior of exhaust tube 30.

In conventional tungsten halogen lamps using foil seals, the degree of melting of the envelope is less critical than in direct lead wire sealing. Since the degree of melting is less critical in the foil seal applications, it is possible to seal an exhaust tube into the lead wire seal area without closing the exhaust tube. However, this is not the case in applications having a direct or straight through lead wire seal. Accordingly, it is difficult to'obtain a hermetic seal and maintain the exhaust tube in an open condition. Fires which would allow the exhaust tube to stay open would not form a good seal and fires which formed a good seal would close the exhaust tube. Prior to and during the sealing operation, nitrogen flows from conduit 43 through passage 44 in exhaust tube 30 into bulb 40 to prevent the lamp parts from oxidizing when the fires are applied to the envelope.

Retractable flush capillary tube 61 is placed inside sealed lamp 39, as shown in FIG. 7, and the flow of nitrogen through the envelope and out the lower end 45 of exhaust tube 30 continues until the envelope is free of impurities. Two-way valve 46 closes nitrogen conduit 56 and opens fill gas conduit 57 to allow a preselected fill gas to flow into lamp 39. The fill gas used in making one of the types of lamps of the invention contains 98.95 percent by volume of krypton, 0.05 percent by volume of oxygen, and 1 percent by volume of methyl iodide (Cl-I l).

Having filled the sealed lamp 39 with the desired fill gas, flush capillary tube 61 is retracted to a point below location 49 and tipping fires 48 long tip or seal the exhaust tube at a desired location such as 49.

Lamp 39 may be tipped at any location along exhaust tube 30 up to the lower edge 50 of spiral 28. The lamp illustrated in FIG. 7 will be pressurized and therefore is tipped at 49 so that the volume of fill gas contained in the exhaust tube can be moved into the envelope during a subsequent short tipping operation shown in FIG. 8.

Referring now to FIG. 8, container 51 is filled with a coolant 52, such as liquid nitrogen. Lamp 39 is immersed in the coolant 52, and the fill gas from the exhaust tube and the bulb 40 condense in the colder portion 53 of the bulb. After a brief period of time to allow the fill gas to condense in the colder portion of the bulb, tires 54 heat exhaust tube 30 at location 55 to tip the exhaust tube for the second time thereby decreasing the volume of the exhaust tube. The resultant decreases in volume for a fixed quantity of fill gas raises the pressure within lamp 39..

As indicated earlier, the fill gas contains methyl iodide (CI-I 1). It has been found in certain applications that, if methyl iodide is not cracked before the lamp is used, it will crack when the filament is lighted and it is believed that carbon from the methyl hydrocarbon will combine with the tungsten filament to form a eutectic which reduces the melting temperature of the tungsten wire to below the lamp-operating temperature.

One method of cracking the carbon is illustrated in FIG. 9. Lamp 39 is placed near semicircular probe 47 of a high frequency coil, not shown, and an arc is formed between the bottom portion 59 of lead wire 34 and the probe 47. The energy of the arc breaks down the methyl iodide thereby freeing the iodine for the halogen cycle. ln the medical and optical applications mentioned earlier, it is important that the are be struck near the seal area because the cracking creates a residue which discolors the bulb wall and would be quite harmful if it were located in the near vicinity of the rounded end.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. An incandescent lamp comprising: an envelope of high temperature aluminosilicate glass comprising by weight percent between 59 and 70 percent SiO to percent A1 0 and 7.4 to 28 percent BaO, said envelope also having a rounded end, refractory metal lead wires hermetically sealed into said envelope at one end of said envelope opposite said rounded end, a tungsten filament connected at each end to said lead-in wires, said envelope containing the tipped-off residue of an exhaust tube located at the end of the envelope opposite the rounded end, said tipped-off residue containing a refractory metal spiral for keeping the exhaust tube open while said lead-in wires are hermetically sealed in said envelope, and a filling within said envelope containing an'inert gas and a halogen.

2. An incandescent lamp as claimed in claim 1 wherein said refractory metal lead wires and said spiral are tungsten.

3. An incandescent lamp as claimed in claim 1 wherein said rounded end of said envelope contains a lens.

4. An incandescent lamp as claimed in claim 1 wherein said halogen is a quantity of iodine.

5. An incandescent lamp as claimed in claim 4 wherein said refractory metal lead wires are molybdenum and said refractory metal spiral is tungsten.

6. An incandescent lamp as claimed in claim 5 wherein said iodine is added to the lamp in the form of methyl iodide.

7. An incandescent lamp as claimed in claim 6 wherein said quantity of iodine is equal to 1 percent by volume.

8. A method of manufacturing an incandescent lamp comprising:

a. inserting a refractory metal spiral into an exhaust tube,

b. heating the exterior of the exhaust tube lightly in the area where the spiral is located,

c. attaching a filament to refractory metal lead wires to form a mount,

d. positioning said mount over said exhaust tube such that said lead wires straddle the exterior of said exhaust tube in the area of the refractory metal spiral,

e. positioning a rounded end bulb over said mount and said exhaust tube,

f. heating said envelope, lead wires, and the exhaust tube to seal the lead wires and the outer periphery of the exhaust tube to the bulb at the bulbs open end to form a sealed lamp.

g. flushing said sealed lamp with an inert gas to remove impurities,

h. filling said lamp with a fill gas,

i. heating said exhaust tube, to form a tipped sealed tube, at a location below said spiral to form a sealed exhausted lamp.

9. The method claimed in claim 8 wherein said heating and tipping operation is followed by cooling of said lamp at said rounded end so that said fill gas is condensed in the rounded end portion of the bulb, heating said tipped-off residue at a location near the end of said spiral to form a pressurized sealed and exhausted lamp.

10. The method claimed in claim 8 wherein said fill gas contains a halogen hydrocarbon and said heating and tipping operation is followed by cracking carbon from said halogen hydrocarbon. 

2. An incandescent lamp as claimed in claim 1 wherein said refractory metal lead wires and said spiral are tungsten.
 3. An incandescent lamp as claimed in claim 1 wherein said rounded end of said envelope contains a lens.
 4. An incandescent lamp as claimed in claim 1 wherein said halogen is a quantity of iodine.
 5. An incandescent lamp as claimed in claim 4 wherein said refractory metal lead wires are molybdenum and said refractory metal spiral is tungsten.
 6. An incandescent lamp as claimed in claim 5 wherein said iodine is added to the lamp in the form of methyl iodide.
 7. An incandescent lamp as claimed in claim 6 wherein said quantity of iodine is equal to 1 percent by volume.
 8. A method of manufacturing an incandescent lamp comprising: a. inserting a refractory metal spiral into an exhaust tube, b. heating the exterior of the exhaust tube lightly in the area where the spiral is located, c. attaching a filament to refractory metal lead wires to form a mount, d. positioning said mount over said exhaust tube such that said lead wires straddle the exterior of said exhaust tube in the area of the refractory metal spiral, e. positioning a rounded end bulb over said mount and said exhaust tube, f. heating said envelope, lead wires, and the exhaust tube to seal the lead wires and the outer periphery of the exhaust tube to the bulb at the bulb''s open end to form a sealed lamp. g. flushing said sealed lamp with an inert gas to remove impurities, h. filling said lamp with a fill gas, i. heating said exhaust tube, to form a tipped sealed tube, at a location below said spiral to form a sealed exhausted lamp.
 9. The method claimed in claim 8 wherein said heating and tipping operation is followed by cooling of said lamp at said rounded end so that said fill gas is condensed in the rounded end portion of the bulb, heating said tipped-off residue at a location near the end of said spiral to form a pressurized sealed and exhausted lamp.
 10. The method claimed in claim 8 wherein said fill gas contains a halogen hydrocarbon and said heating and tipping operation is followed by cracking carbon from said halogen hydrocarbon. 